Visual evoked potentials in children with neurofibromatosis type 1

The purposes of this investigation were to determine: (a) if visual evoked potential (VEP) abnormalities could be identified in children with neurofibromatosis type 1 (NF1) with no evidence of optic pathway or brain neoplasias on MRI; and (b) if VEP abnormalities could be explained by the presence of hyperintense T2-weighted foci on MRI testing, known as unidentified bright objects (UBOs). To answer these questions, VEPs were recorded from 16 children with NF1 and compared to 13 normal subjects in the same age range tested with the same protocol. Pattern-reversal VEPs were recorded at four stimulus sizes both monocularly and binocularly, the latter to hemi-field stimuli. Flash VEPs were recorded in dark- and light-adapted conditions. VEP measurements and MRI readings for UBOs were conducted in a masked fashion. Ten of the 16 children with NF1 had abnormal VEPs to at least one of the four types of stimuli. Abnormalities included delayed responses (n=6), absent flash VEP P2 component (n=3), or both (n=1). Abnormalities of the P2 component of the dark-adapted flash VEP were the most common finding (n=7), although no single testing strategy was able to identify all children with abnormal VEPs. UBOs were present in all children, demonstrating that their presence does not fully account for VEP abnormalities in children with NF1. This study also demonstrates that VEP abnormalities are present also in the absence of neoplasias of the optic pathways or of the brain. Our results are suggestive of a primary abnormality of visual processing in children with NF1.